The present invention relates to articles made from the conversion of multilayer films, and particularly to such articles which are suitable for packaging meat products, especially for the cook-in packaging of meat products wherein the film has a food contact surface which adheres to the meat during cook-in.
For several years, the food packaging industry has utilized a packaging film from which bags and casings have been made which are of improved structural soundness such that they have been fully characterized as cook-in. A precooked food product has been attractively packaged using a film within which the product was precooked. The film has been used primarily for cook-and-ship end-use, wherein a meat product is packaged in the film and cooked while in the film, and is thereafter cooled and shipped to wholesaler, retailer, or consumer, without being overwrapped and without having the film stripped therefrom and thereafter being re-packaged in another film.
The phrase xe2x80x9ccook-inxe2x80x9d as used herein refers to the process of cooking a product packaged in a material capable of withstanding exposure to long and slow cooking conditions while containing the food product, for example cooking at 57xc2x0 C. to 121xc2x0 C. (i.e, 135xc2x0 F.-250xc2x0 F.) for 2-12 hours, preferably 57xc2x0 C. to 95xc2x0 C. (i.e 135xc2x0 F.-203xc2x0 F.) for 2-12 hours. Cook-in packaged foods are essentially pre-packaged, pre-cooked foods which may be directly transferred to the consumer in this form. These types of foods may be consumed with or without warming. Cook-in packaging materials maintain seal integrity, i.e., any heat sealed seams should resist being pulled apart during cook-in, and are conformable to the contained food product. Preferably, conformability is achieved by the film being heat shrinkable so as to form a tightly fitting package. Additional optional characteristics of films for use in cook-in applications include delamination-resistance, low O2-permeability, heat-shrinkability, and optical clarity.
Cook-in films preferably have a tendency for adhesion to the food product, thereby preventing xe2x80x9ccook-outxe2x80x9d, i.e., xe2x80x9cpurgexe2x80x9d, which is the collection of juices between the outer surface of the food product and the meat-contact surface of the film, i.e., the surface in direct contact with the meat. This meat adhesion characteristic of the meat contact layer serves to both prevent cook-out (and thereby prevent an unattractive package or the need to strip the film from the meat and repackage the meat), to increase product yield, and to prevent the meat from losing juices which improve its edible character. As used herein, the term xe2x80x9cadherexe2x80x9d, with respect to meat-adhesion, refers to a meat-contact surface of the film which bonds during cook-in to the contained food product to an extent sufficient to substantially prevent accumulation of fluids between the film and the contained meat product.
However, some of the cook-in films in commercial use have an outer layer which serves as a meat-adhesion layer, this layer containing a relatively large amount of one or more relatively expensive polyamides. In one commercially available film, for example, this outer polyamide layer typically comprised a blend of polyamide 12 and polyamide 6/12, both of which are relatively expensive but which provide advantageous sealing and meat adhesion performance. It has been believed that these polyamide polymers must be present in a relatively thick outer layer (e.g., about 20% of the total film thickness), in order to provide the seal performance during cook-in, because the converted articles typically need to survive cooking for long periods of time at high temperatures, e.g., cooking the meat product at 190xc2x0 F. for 6-12 hours. It would be desirable to reduce the cost of the film if the seal quality and meat-adhesion could be maintained, or at least not sacrificed to any significant degree.
In comparison with prior art commercially-available films, the article of the present invention utilizes a film which contains less costly polymer, while providing comparable performance characteristics, i.e., comparable seal strength, comparable meat adhesion, and comparable package appearance. Furthermore, in some cases this film can provide the further advantage of downgauging of the total film thickness, so that less total polymer is required. Furthermore, in some cases the film of the present invention can be used to provide an enhanced level of shrink tension. In some cases, the film of the present invention can provide enhanced toughness/abuse resistance even though the thickness of the film is not increased over other films which have previously been used. Surprisingly, the film of the present invention can provide comparable performance characteristics even if it has a thickness less than the cook-in films which have been in commercial use. In addition, the film of the invention exhibits improved heat seal strength relative to prior art commercially-available films having, for example, ionomer meat contact layers. The film of the present invention is suitable for the packaging of a wide variety of food products, especially meat products.
As a first aspect, the present invention is directed to an article comprising a multilayer film. The multilayer film comprises: (A) a first layer comprising a polyamide having a melting point of from about 250xc2x0 F. to 400xc2x0 F., the first layer having a thickness of less than about 18 percent, based on a total thickness of the multilayer film; (B) a second layer comprising at least one member selected from the group consisting of polyamide 6, polyamide 9, polyamide 10, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 612, polyamide 6I, polyamide 6T, polyamide 69, and copolymers thereof, the second layer having a thickness of from about 3 to 30 percent of the total thickness of the multilayer film; and; and (C) a third layer which serves as an O2-barrier layer and comprises at least one member selected from the group consisting of ethylene/vinyl alcohol copolymer, polyamide, polyvinylidene chloride, and polyalkylene carbonate. The first layer is sealed to itself. Preferably, the first layer has a thickness of from about 0.5 to 18 percent of the total film thickness; more preferably, from about 5 to 18 percent; still more preferably, from about 6 to 15 percent; and, yet still more preferably, from about 8 to 12 percent. Preferably, the polyamide in the first layer has a melting point of from about 300xc2x0 to 375xc2x0 F. Preferably, the second layer has a thickness of from about 3 to 30 percent of the total film thickness; more preferably, from about 4 to 20 percent; still more preferably, from about 5 to 10 percent. Preferably, the second layer is directly adhered to the first layer. Preferably, the second layer comprises at least one member selected from the group consisting of polyamide 6, polyamide 66, and polyamide 6/66.
In a first preferred embodiment, the first layer comprises only one polyamide. In a second preferred embodiment, the first layer comprises copolyamide 6/12 in an amount of from about 20 to 80 weight percent, and polyamide 12 in an amount of from about 80 to 20 weight percent. In either embodiment, the first layer preferably has a thickness of less than about 15 percent, based on a total thickness of the multilayer film. In either embodiment, preferably the first layer has a thickness of from about 0.2 to 0.4 mil.
Preferably, the second layer comprises polyamide 6 and at least one member selected from the group consisting of polyamide 66, polyamide 610, polyamide 6/12, polyamide 6I, polyamide 6T, polyamide 69, and copolyamides thereof. More preferably, the second layer comprises polyamide 6 in an amount of from about 40 to 90 weight percent, and polyamide 6/12 in an amount of from about 10 to 60 weight percent.
Preferably, the thickness of the second layer is from about 3 to 20 percent, based on a total thickness of the multilayer film; more preferably, the thickness of the second layer is less than about 15 percent, based on a total thickness of the multilayer film.
Preferably, the multilayer film further comprises a fourth layer comprising at least one member selected from the group consisting of polyolefin, polyamide, polyester, starch-containing polymer, polystyrene, and polyurethane. Preferably, the fourth layer comprises at least one member selected from the group consisting of polyethylene homopolymer, polyethylene copolymer, polypropylene homopolymer, polypropylene copolymer, polybutene homopolymer, and polybutene copolymer, and the fourth layer is an outer layer.
Preferably, the multilayer film further comprises a fifth layer between the third layer and the fourth layer, the fifth layer serving as a tie-layer. Preferably, the multilayer film further comprises a sixth layer between the first layer and the third layer, the sixth layer serving as a tie-layer.
Preferably, the multilayer film is biaxially oriented. Preferably, the multilayer film has a free shrink, at 185xc2x0 F., of at least 10 percent in at least one direction.
Preferably, at least a portion of the multilayer film comprises a cross-linked polymer network.
As a second aspect, the present invention is directed to a bag comprising a multilayer film as in the first aspect of the present invention. Preferably, the bag is an end-seal bag or a side seal bag. Preferably, the multilayer film in the bag is a preferred multilayer film in accordance with the first aspect of the present invention.
As a third aspect, the present invention is directed to a packaged product comprising a package and a product in the package. The package comprises the multilayer film as set forth in the first aspect of the present invention. The product comprises cooked meat. Preferably, the multilayer film in the package is a preferred multilayer film in accordance with the first aspect of the present invention. Preferably, the cooked meat product comprises at least one member selected from the group consisting of poultry, ham, roast beef, liver sausage, mortadella, bologna, goat, and lamb. More preferably, the cooked meat product comprises at least one member selected from the group consisting of poultry, ham, and roast beef.